Since the turn of this century, the automotive industry has allocated limited funds for the research and development of alternative power sources, including electric vehicles. These efforts have proven unsuccessful, however, due to technical and economic obstacles.
On the technical side, those skilled in the art will recognize that conventional electric vehicles have historically suffered from the inability to meet performance and range requirements necessary for practical use. For example, it is well known that significant pulse power is required to meet vehicle acceleration requirements during peak power demands. In order to meet these power demands, battery designers have been forced to trade-off battery specific energy (energy per unit weight) and power density (power per unit volume). As a result, larger and heavier batteries have been utilized which have decreased efficiency, performance and aesthetic appeal. These design problems coupled with the availability of inexpensive imported fossil fuels have heretofore impeded large-scale commercial development and implementation of electric vehicles.
Recent changes, however, in global politics and legislation mandating reduced emission automobiles have now fueled renewed interest in the development of electric and hybrid internal combustion engine/electric vehicles which are "environmentally safe". See for example, U.S. Pat. No. 4,165,795 to Lynch et al. which discloses a parallel hybrid drive system for self propelled vehicles having a drive shaft in common with an internal combustion engine leading to a variable speed transmission and a final drive train.
Similarly, U.S. Pat. No. 3,923,115 issued to Helling discloses a parallel hybrid drive for use in a vehicle having at least two motors, one of which is an electric motor. Helling further discloses the an electric accumulator for use in cooperation with a gyro-accumulator drive (flywheel) in a 3-shaft configuration with multiple differentials and speed matching capability for storing kinetic energy during braking.
U.S. Pat. No. 4,438,342 issued to Kenyon discloses a hybrid electrical-heat engine vehicle and alternator which is totally free of elemental iron in its magnetic circuit. As disclosed, the rectified output of the alternator can be provided in series with a battery pack powering an electric drive motor so as to give a surge of mechanical power without magnetic saturation loss.
U.S. Pat. No. 4,305,254 issued to Kawakatsu et al. discloses a control apparatus for a hybrid vehicle comprising an internal combustion engine (ICE) and a motor/generator energized by a battery. As more fully disclosed in Kawakatsu, the ICE is designed to run only in a predetermined region of better fuel consumption and torque range. Outside this region, the motor is mainly used as a prime mover.
Finally U.S. Pat. No. 3,791,473 issued to Rosen discloses a hybrid power train which includes a heat engine operating as a prime mover in cooperation with a secondary electromechanical system such as a battery energized electric motor. As disclosed by Rosen, the heat engine is a quasi-constant torque device which can be varied in response to the state of charge of the battery or in response to operator imposed torque demands in excess of certain predetermined amounts. The power train further includes a mechanical accelerator for controlling the instantaneous torque output of the combined heat engine/electric motor.
The prior art systems discussed above provide a general background in respect of the design and application of hybrid drive systems in electric vehicles. Although these systems generally have increased range and acceleration capabilities due to improved materials and battery designs, they still suffer from design and operational restraints reminiscent of predecessor electric vehicles. More specifically, the prior art hybrid systems still require significant secondary power capability to meet acceleration and extended range requirements. These deficiencies are compounded further in situations where the vehicles are required to operate in pure EV (non-emission) modes as will soon be required in California and several other states which have adopted similar zero emission plans.